A number of heterocyclic bisphosphonic acid derivatives useful in treating disorders of calcium metabolism such as Morbus Paget, osteoporosis, Morbus Bechterew, arthritis, etc. have appeared in the literature. Exemplary of these compounds are the pyrrolidone-5,5-diphosphonic acid derivatives disclosed in Belgian Patent 819,187, granted Feb. 26, 1975; the piperidinone diphosphonic acid derivatives of German Offenlegungsschrift 25 53 963, published Jun. 6, 1977 and the oxazine bisphosphonic acid disclosed in German Offenlegungsschrift 37 19513, published Dec. 22, 1988.